Anti oxidants

ABSTRACT

A NON-CORROSIVE ANTIOXIDANT MIXUTRE SUITABLE FOR ADDITION TO AN AIRCRAFT LUBRICATING OIL COMPRISING (A) TWO TO TEN PARTS BY WEIGHT OF A COMPOUND OF THE FORMULA   (((R)N-PHENYL)-NH-)NAPHTHALENE   WHERE N IS AN INTEGER, AND R IS AN ALKYL GROUP CONTAINING AT LEAST THREE CARBON ATOMS (E.G. OCTYL PHENYL-B-NAPHTHYLAMINE), AND (B) ONE PART BY WEIGHT OF A PHENYLENE DIAMINE OF THE FORMULA   (4-(X1-NH-)PHENYL)-NH-X2, OR 1-(X1-NH-),2-(X2-NH-)BENZENE   WHERE X1 AND X2 ARE HYDROCARBYL GROUP OR THE GROUP R1COOR4- WHERE R1 AND R4 ARE HYDROCARBYL GROUPS (E.G. N-PHENYL, N1-CYCLOHEXYL-P-PHENYLENE DIAMINE).

"United States Patent @jfi US. Cl. 252-515 R 13 Claims ABSTRACT OF THE DISCLOSURE A non-corrosive antioxidant mixture suitable for addition to an aircraft lubricating oil comprising (A) two to ten parts by weight of a compound of the formula where n is an integer, and R is an alkyl group containing at least three carbon atoms (e.g. octyl phenyl-p-naphthylamine), and (B) one part by weight of a phenylene diamine of the formula where X and X are a hydrocarbyl group or the group R COOR where R and R are hydrocarbyl groups (e.g. N-phenyl, N -cyclohexyl-p-phenylene diamine).

This invention relates to a mixture of compounds suitable as an antioxidant, especially for lubricating oils.

Although many antioxidants have been proposed, especially for lubricating oils such as aircraft lubricating oils, hitherto many antioxidants although meeting specification requirements have often caused other problems, e.g. corrosion. Thus antioxidants for synthetic ester lubricants for aircraft have sometimes contained thioamides as one of its components, but the presence of such thioamides has been found to lead to corrosion problems.

We have now found an antioxidant which does not have the disadvantages of corrosion caused by such thioamidecontaining antioxidants. According to this invention an antioxidant mixture comprises (A) two to ten parts by weight of a compound of the formula QG Q- where n is an integer, and the group R or each group R which can be the same or different is an alkyl group containing at least three carbon atoms, and (B) one part by weight of the phenylene diamine of the formula DONE-@NHXQ or where X and X are the same or different and are a hydrocarbyl group or the group R COOR where R and R are hydrocarbyl groups.

Component (A) is an alkyl phenyl-u-naphthylamine, or an alkyl phenyl-B-naphthylamine. It is preferable that the group (R) or one of the groups (R) is in the para position, and the chain length of any alkyl group is preferably between 5 and 12 carbon atoms. Examples of suitable alkyl groups are propyl, butyl, hexyl, octyl, decyl,

Patented Sept. 25, 1973 or dodecyl. If there is more than one alkyl group R, then the total number of carbon atoms in the alkyl groups is preferably no more than 20.

The preferred example of component (A) is octyl phenyl-,B-naphthylamine.

Regarding component (B) when the groups X and X are hydrocarbyl groups, they can be alkyl, cycloaliphatic, aryl, alkaryl, or aralkyl groups. They could also be ethylenically unsaturated groups, e.g. alkenyl groups, but saturated groups are preferred. Suitable examples of alkyl groups are C to C alkyl groups, e.g. methyl, ethyl, isopropyl, methylpentyl, octyl, dodecyl, hexadecyl, or eicosyl. Cycloaliphatic groups which may be used include cyclopentyl, cyclohexyl, and cyclooctyl groups. Also substituted cyclo groups can be used, e.g. methyl cyclopentyl, and propyl cyclo octyl. Suitable aryl groups include phenyl, naphthyl, and anthranyl. Alkaryl groups which may be used include methyl phenyl, propyl phenyl, and other alkyl groups in which the alkyl substituent contains 1 to 10 carbon atoms. Examples of aralkyl groups are benzyl, phenyl ethyl, and 3-phenyl hexyl.

The group R is divalent and may be aliphatic or it may include a benzene ring. When R is aliphatic one or both of the groups X and X may be R CO(CH where R is a hydrocarbyl group and p is an integer. The group R is preferably an alkyl group, and preferably has a chain length of from 2 to 10 carbon atoms. The integer p is preferably from 2 to 10, e.g. 2 to 5 inclusive.

Specifically component (B) can be a compound of the formula or a compound of the formula where R is a hydrocarbyl, preferably alkyl group, or R COO(CH and R is a hydrocarbyl, preferably alkyl group or R COO(CH2)p-.

Generally it is preferable if one of the groups X and X is alkyl or cycloalphatic, and the other is aryl or alkaryl. Also the para phenylene diamines are preferred. A preferred example of component (B) is N-phenyl-N cyclohexyl-p-phenylene diamine, but other examples which can be used are his (ethyl, methyl pentyl) pphenylene diamine, and diphenyl-p-phenylene diamine.

The weight ratio of components (AzB) is respectively between 2:1 and 10:1, and the preferred weight ratio of A:B is from 3:1 to 6:1.

The lubricating oil to which the antioxidant mixture may be added can be any mineral, animal, fish, vegetable or synthetic oil, for example, petroleum fuel fractions ranging from naphthas to spindle oil to SAE 30, 40 or 50 lubricating oil grades, castor oil, animal or fish oils or oxidized mineral oil, e.g. palm oil, lard oil, tallow oil, arachis oil or sperm oil.

The preferred lubricating oil is a synthetic ester and suitable diesters include diesters of the general formula ROOCR'COOR and RCOOR'OOCR where R represents a C to C alkyl group, while R represents a C to C saturated aliphatic hydrocarbon group or an ether-interrupted saturated aliphatic hydrocarbon group. The above types of esters may be prepared from alcohols and dicarboxylic acids or glycols and monocarboxylic acids.

Another suitable class of ester lubricant are the polyesters which are prepared by reacting polyhydric alcohols, e.g. those having 2 to 12 hydroxyl groups per molecule and 2 to 40 carbon atoms per molecule, such as trimethylolpropane, pentaerythritol and dipentaerythritol with monoand/or di-carboxylic acids such as butyric acid, caproic acid, caprylic acid and pelargonic acid, or adipic, sebacic or azelaic acids.

The complex esters which may be used as base oils are formed by esterification reactions between a dicarboxylic acid, a glycol and an alcohol and/or a monocarboxylic acid. These esters may be represented by the following formulae:

wherein R represents alkyl radicals derived from a monohydric alcohol, R represents hydrocarbon radicals derived from a dicarboxylic acid, e.g. alkanedioic acids, R represents divalent hydrocarbon or hydrocarbon-oxy radicals such as derived from an alkylene glycol or polyalkyleneglycol, while R represents the alkyl group derived from a monocarboxylic acid. It in the complex ester molecule which is an integer will usually range from 1 to 6 depending upon the product viscosity desired which is controlled by the relative molar ratio of the glycol or polyglycol to the dicarboxylic acid. In preparing the complex ester, there will always be some simple ester formed, i.e. n=0, but this will generally be a minor portion. In general these complex esters will have a total of between 15 and 80, e.g. between 20 and 65 carbon atoms per molecule.

Particularly suitable lubricants are esters of polyhydric alcohols having the formulae where R is a CH OH group or an alkyl group, e.g. an alkyl group containing 1 to 6 carbon atoms. Thus, suitable esters of this type are the neopentyl polyol esters of trimethylol ethane, trimethylol propane, trimethylol butane and of pentaerythritol or di-pentaerythritol.

The preferred acids used to esterify trimethylol propane are the C to C monocarboxylic acids. Particularly preferred are the C C esters, e.g. C (caprylic) and C (pelargonic) acid esters. Mixtures of these C C acids may be used. When such an acid mixture is used, it is ferred are the C C esters, e.g. C (caprylic) and C Although more difiicult to form, it is even more preferred that one methylol group be esterified with a neo-heptanoic acid, e.g. 2,2-dimethylpentanoic acid, and the remaining methylol groups esterified with non-hindered acids, e.g. pelargonic acid. This particular ester is substantially as thermally stable as the completely hindered ester but has superior volatility and low temperature characteristics.

The preferred acids used to esterify pentaerythritol are the C C monocarboxylic acids with the more preferred esters being those of C to C acids, e.g. n-valeric, isovaleric, 2-ethyl butyric, caproic, n-heptylic, n-octanoic or 2-ethyl hexoic acids or a mixture of C to C acids.

Blends of diesters with minor proportions of one or more thickening agents may also be used as lubricants. Thus one may use blends containing up to 50% by volume of one or more water insoluble polyoxyalkylene glycols, for example, polyethylene or polypropylene glycol, or mixed oxyethylene/oxypropylene glycol.

Formulations suitable for gas turbine lubrication include from 65 to 90 vol. percent of one or more diesters of azelaic or sebacic acid and a C -C branched chain alcohol, particularly of 2-ethyl hexanol, or x0 alcohols consisting predominantly of C C or C alcohols, or o m tu es of such al oh a d 3 to 1 of p yoxyalkylene glycol ether represented by the general formula:

wherein R R and R are hydrogen or C C alkyl groups and wherein not more than two such groups is hydrogen, and n is an integer greater than 1. Particularly useful compounds are poly-oxypropylene glycol monoethers and the corresponding diethers.

The thermal stability of such diester/polyoxyalkylene glycol ethers may be improved if a small proportion of a complex ester derived from three or more carboxylic acids or alcohols, at least two of which are difunctional acids or alcohols is incorporated. Such complex esters may be glycolor dicarboxylic acid centered, the molecule being terminated with a mono-hydroxy or mono-carboxylic acid compound. A particularly preferred complex ester of this type is derived from polyethylene glycol of molecular weight 200, 2 molecules of sebacic or azelaic acid, and 2 molecules of a C -C branched chain aliphatic monohydric alcohol, particularly 2-ethyl hexanol.

The total quantity of the antioxidant mixture added to the lubricating oil can vary but is preferably between 0.001 and 10.000 wt. percent, e.g., between 0.01 and 5.00 wt. percent.

Other additives which may be incorporated in the lubricating oil include corrosion inhibitors, e.g. sebacic acid, a metal deactivator such as quinizarin, a foam inhibitor, e.g. a silicone polymer such as dimethyl silicone, or an antiwear additive, e.g. neutral aryl phosphates such as tricresyl phosphate, neutral alkyl aryl phosphates, or neutral phosphonates.

EXAMPLE I RES ULTS Temperature 215 C. for 192 hr.

Induction Percent period Antioxidant (wt. percent) volatility (hr.)

2.0POPD 54.7 2.0 PBNA 50. 6 24 1.0 PCPD 1.0 PBNA... 56.1 52 1.0 PCPD 2.0 PBNA 39. 5 92 1.0 PCPD 3.0 PBNA 33. 4 1.0 PCPD +3.2 PBNA 26.2 102 EXAMPLE 11 Different amounts of diphenyl-p-phenylene diamine (DPPD) and mono-octyl phenyl 3 naphthylamine (PBNA) were added to the same ester used in Example 1 containing 1 wt. percent of tricresyl phosphate. Their performance as antioxidants was assessed by the procedure of Example 1.

1 This test involves 1passing air saturated with water vapour at 250 111]. minute through 50 m oil heated to the required temperature in a glass vessel. The percentage volatility as a measurement of the effectivenes s of the antioxidant, and the induction period is found by plotting percent volatility ersus time.

EXAMPLE III Dilferent amounts of bis(octyl)-p-phenylene diamine (BOPD) and monooctyl-phenyl ,3 naphthylamine were added to the same ester used in Example I containing 1% tricresyl phosphate. Their performance as antioxidant was assessed by a procedure similar to that used in Examples I and II except that the test took 72 hours instead of 192 hours.

RESULTS Temperature 215 C. for 72 hr.

Induction Percent period Antioxidant (wt. percent) volatility (hr.)

EXAMPLE IV In this example a comparison was made using PBNA in conjunction with a thioamide and in conjunction with PCPD'.

The base oil was the same as that used in Example I and also contained 1% tricresyl phosphate (TCP) and 0.3% of anthranilamide as a corrosion inhibitor.

In order to achieve the same oxidative stability of the oil it was found necessary to use in addition to 2% by weight of octyl phenyl-fi-naphthylamine, 0.1% by weight of didodecyl thiourea on the one hand, and 1% by weight of N-cyclohexyl-p-phenylene diamine on the other hand. As can be seen from the results of the Rolls Royce corrosion test (RR Method 1002 Procedure A) even with ten times as much,PC-PD compared with thiourea, the corrosion which results is far less.

The Rolls Royce Corrosion Test Method 1002 is carried out by heating the oil at 200 C. for 192 hours in the presence of metals typical of those found in aircraft turbine engine systems. The quality of the oil is assessed from the resultant corrosion (change in weight) of the metal specimens.

What is claimed is: 1. An antioxidant mixture comprising (A) two to ten parts by weight of a compound of the formula where n. is an integer, and the group R or each group R which can be the same or different is an alkyl group containing at least three carbon atoms, and (B) one part by weight of diamine selected from a phenylene diamine of the formula XlNH NHX2 and X NHQ where X and X are the same or dilferent and are a hydrocarbyl group or the group R COOR where R and R are hydrocarbyl groups.

2. A mixture according to claim 1 where the group (R) or one of the groups (R) of component (A) is in the para position.

3. A mixture according to claim 1 wherein there are more than one alkyl group (R) in component (A) and the total number of carbon atoms in the alkyl groups is not more than 20.

4. A mixture according to claim 1 wherein component (A) is octyl phenyl-B-naphthylamine.

5. A mixture according to claim 1 wherein the groups X and X of component (B) are saturated.

6. A mixture according to claim 5 wherein either or both the groups X and X are selected from the groups consisting of cycloaliphatic, aryl, alkaryl and C to C alkyl.

7. A mixture according to claim 1 wherein the group R COOR is the group R COO(CH where p is an integer.

8. A mixture according to claim 1 wherein component (B) is a diamine selected from a compound of the formula Where R is a hydrocarbyl group or the group R COO(CH and R is a hydrocarbyl group or the group R COO(CH and References Cited UNITED STATES PATENTS 3,347,791 10/1967 Thompson et a1 25250 3,535,243 10/ 1970 Chao et a1. 252-50 3,655,562 4/1972 Chao et a1. 252-50 3,660,290 5/1972 Schlobohm 252-50 WERTEN F. W. BELLAMY, Primary Examiner US. Cl. X.R. 252=-50 

